U.S. Pat. No. 5,394,812, issued Mar. 7, 1995, discloses one prior art approach for injecting a small quantum of gel-like substances of hydrophilic material into the ground as discrete cylindrical hydrophilic slugs deployed in a uniform pattern. Upon penetration in the soil, and especially when the slugs of material reach a soil change or gradient, the hydrophilic material stops its advancement into the soil substrate and either fans out or remains in its initial configuration.
Other known techniques for dispensing hydrophilic polymer material involve mixing the polymer with water in an injection pump which directly receives the polymer. Water is then pumped therein under high pressure. This approach stresses the equipment since the polymer may clump up when mixed, particularly when the dispensing is to be throttled on and off. Yet another prior art approach involves administering the polymer in a liquid solution as a uniform continuous steam into the ground. High pressures are involved in such distribution systems and the equipment employed is prone to failure because it cannot simultaneously and continuously achieve the force required to accurately penetrate the soil.
It is also known to treat sod, such as that employed on golf courses, with polymer by slicing into the sod with a disc-like implement or injecting a liquid ribbon. Use of a disc requires subsequent replacement of the soil over the polymer and such an approach imposes a limitation on the distance between rows of polymer. Linear ribbon application, on the other hand, causes sod to swell in a non-uniform manner, possibly providing undesirable undulations on the surface.
Referring once again to the arrangement disclosed in U.S. Pat. No. 5,394,812, such patent provides an arrangement for mixing polymer in water and then injecting the mixture through the soil. A storage tank supported on a trailer receives a combination of polymer and water. A pump receives the mixture and delivers it through a high pressure hose to an outlet distribution device including a plurality of nozzles supported from a wheeled carriage frame.
The mixture is injected into the soil by periodic pulsing of a solenoid type valve so that upon opening of the valve, the mixture is injected under high pressure into the soil. When the valve is closed, a pressure bleed-off returns the mixture to the tank for agitating the mixture in the tank. Such an arrangement involving recirculation of the mixture not only adds to the complexity of the apparatus but can damage, such as by shredding, the polymer material, rendering it less effective when applied to the soil. Furthermore, such an arrangement necessarily requires a relatively high water to polymer ratio in the mixture resulting in inefficient delivery of the polymer to the soil.
The following additional patents are also believed to be representative of the present state of the prior art in this field: U.S. Pat. No. 5,370,069, issued Dec. 6, 1994, U.S. Pat. No. 5,303,663, issued Apr. 19, 1994, U.S. Pat. No. 5,101,745, issued Apr. 7, 1992, U.S. Pat. No. 5,291,842, issued Mar. 8, 1994, U.S. Pat. No. 4,009,666, issued Mar. 1, 1977, U.S. Pat. No. 3,875,876, issued Apr. 8, 1975, U.S. Pat. No. 4,903,618, issued Feb. 27, 1990, U.S. Pat. No. 4,034,686, issued Jul. 12, 1977, U.S. Pat. No. 3,331,340, issued Jul. 18, 1967, U.S. Pat. No. 3,330,070, issued Jul. 11, 1967, U.S. Pat. No. 2,930,334, issued Mar. 29, 1960, U.S. Pat. No. 4,807,544, issued Feb. 28, 1989, U.S. Pat. No. 4,903,618, issued Feb. 27, 1990, and U.S. Pat. No. 4,907,516, issued Mar. 13, 1990.